The present invention relates generally to antennas for use with wireless communication apparatus and, more particularly, to a modular antenna system for use with such wireless apparatus in which the antennas of each module are polarized in different directions.
The computer industry is trending toward the use of wireless technology for use in personal computers, laptop computers, personal digital assistants (“PDA's”) home control centers, computer work stations, printers, facsimile machines, etc. Previously, all these devices involved the use of special cables to connect these various devices together with device-specific software that often used proprietary protocols. In order to effectively communicate with all of these personal electronic devices, a person might need to obtain many different cables for interconnecting the devices together. However, the person had no assurance that all the devices could interconnect.
In 1998, a special interest group known as “Bluetooth” was developed by Intel, IBM, Nokia, Ericsson and Toshiba in order to create a global specification for short range wireless radio frequency (“RF”) communications. This specification was published in 1999 and will be instrumental in the future in achieving interoperability among all kinds of devices, regardless of manufacturer. Hence, Bluetooth is directed toward a technology for the short-range exchange of data. It can be used, for example, to synchronize information between different devices, or to connect Internet linked devices to the Internet without cables. Key to the effective use of Bluetooth technology is a Bluetooth radio module. These modules rely on antennas for effective short range wireless transmittal and receipt of RF signals. Another wireless technology that is being implemented with increasing frequency is the IEEE 802.11 standard that is used to replace wired LANs (Local Area Networks) throughout buildings to thereby permit operation of electronic devices without connecting them to a hard-wired network.
Conventional RF antennas may be used in these applications, but they need to have their structure designed to operate in the high frequency bands (2.4 Ghz) used for Bluetooth and 802.11 communications. Additionally, conventional antennas such as those used on cellular telephones are relatively large and project from the appliance on which they are used, which is undesirable. As a result, the industry has turned to low profile antennas to use in these wireless applications, which include PIFA-style (“planar inverted-F antennas”) antennas.
A typical PIFA antenna includes a planar radiating plate located over a ground plate, which are joined together by a short circuit plate. Such PIFA antennas have low profiles, high efficiency and omni-directional radiation patterns which are particularly suitable for wireless communication applications as described above. However, even the use of these PIFA antennas may create its own set of problems. If the antenna is not positioned correctly in the electronic component, the antenna may be placed in what is known as a “dead spot” where transmitted signals combine with reflected signals that cancel the desired transmitted signal, which condition is also known as a deep fade where transmitted signal levels drop below a detectable level.
A room or other closed environment may have many dead spots, depending on its configuration, and the placement of the wireless device in the environment. It is burdensome on the user to think of the presence of dead spots and locate wireless equipment accordingly. One way to eliminate such dead spots is to utilize multiple antennas that increase signal strength due to spatial diversity or array methods. However, this solution has its own problems in that often the individual radiating elements mutually couple together.
The present invention is directed to a solution to this “dead spot” problem and is directed to an antenna that overcomes the aforementioned disadvantages.